The present invention relates to a method for preparation of diffusion sheets, especially to a low cost and simple method for preparation of diffusion sheets that are abrasion and scratch resistant.
A liquid crystal display (LCD) device includes a backlight module for providing backlight to the LCD device. The backlight module consists of a light source and optical sheet having light guide plate, diffusion sheets and prism sheets. The diffusion sheet is usually attached below the LCD panel, in order to disperse light beams received from the light source and provide uniform light for the LCD panel. The uniform light enables the LCD panel to display a clear image. Conventional diffusion sheet is made by adding a plurality of chemical granules inside substrate (transparent polymer) that work as scattering particles. The diffusion sheet available now includes microparticles dispersed between resin layers. While light beams passing through the diffusion layer, they are reflected and scattered continuingly between the two substrates with different refractive indices so as to achieve light diffusion effect.
Refer to U.S. Pat. No. 6,888,663, after swelling, wetting pretreatment, and interface modification, diffusion particles made from clay is mixed with polymer through a thermal process to produce diffusion sheets. The clay achieves excellent effect (Haze about 80% and light transmittance about 80%) with only a little amount of clay (<3 wt %). Moreover, inorganic material has features of UV resistance, thermal resistance and weather resistance. But the shortcoming is that during the thermal process, the clay may aggregate that leads to reduction of light diffusion and light transmittance.
Refer to U.S. Pat. No. 6,871,994, a light diffusion layer having polymer beads dispersed within a binder is coated on a surface of transparent polymer substrate to form a diffusion film. The beads are transparent and colorless with excellent light transmittance while its shortcomings are poor UV resistance, thermal resistance and weather resistance, all worse than inorganic particles.
Refer to Taiwanese Pat. No. 1237127, a diffusion plate with higher transmittance is disclosed. The diffusion plate features on that an anti-reflective layer is added on an incident surface thereof so that the light transmittance is increased 5%. Yet the disadvantage of this device is that the process for coating the anti-reflective layer increases the cost.
Refer to Taiwanese Pub. No. 200523626, a method for producing diffusion sheet with UV inhibition is disclosed. The advantage of the method is that yellowing and deformation of the diffusion sheet can be avoided after being used. But the UV adsorbent being used are organic materials so that the materials are easy to have degradation after absorbing UV light.
Refer to Taiwanese Pub. No. 200506035, a diffusion plate with high light transmission efficiency and excellent color tone is disclosed. The advantage of this invention is in that the diffusion sheet has excellent thermal resistance and deformation resistance due to organic UV absorbent and stabilizer added during manufacturing processes. The shortcoming is that besides addition of diffusion agents, addition of the UV absorbent and stabilizer will make the whole system more complicated and this has negative effect on stability of the whole system. Moreover, the overall production cost is also increased. Furthermore, after the UV absorbent reacting with UV light, the diffusion sheet is easy to have degradation.